Septic tanks are conventionally equipped with a tile field which receives sewage effluent from a septic tank in a subsurface ground system. The tile absorption field is generally a system of trenches in which are placed lengths of terra cotta or plastic drain pipes with openings in the walls through which the effluent escapes. The pipes are embedded in the bottom of the trenches, which are 30 -36 inches wide, and are covered and surrounded with stone about 10 inches deep and the width of the trench. The stone distributes the escaping effluent evenly to the side walls of the trench, where most of the absorption into the ground takes place.
This type of system has many disadvantages; a three bedroom home on a lot with marginal percolation rate of 60 minutes per inch of fall would require 300 lineal feet of trench and tile with the width of the trench being 3 feet wide. This 900 square foot trench bottom area generally provides storage for the effluent at peak water usage time, however rainwater may cause overloading of the absorption field, thereby causing it to back up into the home or surface on top of the ground. Many home sites (or lots) are not suited for this absorption field, due to topography of the land, size of lot, poor percolation or high water table.
Further the surface trench bottom in this type of absorption field will in time become covered over with a layer of undissolved sewage. When this happens most of the absorption takes place through the side walls of the trench. The undigested sewage will not adhere to the trench wall for long before it will sluff off, thereby keeping the trench walls relatively free of sewage particles. When the trench bottom area does become covered with sewage particles (sewage sludge) the home owner must retrench or replace the absorption field or add additional trenches to compensate for this loss in the absorption area. Additionally, roots may damage the line, or sediment may choke off flow of the effluent through the line, thereby deleteriously affecting the operation of the ground absorption system.
Some effort has been made to overcome some of these problems. For example, in U.S. Pat. No. 3,422,010 to Case a filter bed is formed of specially manufactured cement blocks arranged to provide a plurality of parallel sealed conduits which are connected by elbows to form a continuous pipe line. Such solutions as offered by the Case patent, as well as other attempts to solve the problems attendent to the tile field disposal system have generally been unsuccessful. They are still expensive to install and require much excavation, especially as regards the percentage of ground area to be excavated compared to the area of ground available. Additionally, such systems cannot be maintained or serviced by the home owner. In case of stoppage, the entire filter bed must be dug up and replaced.
Further, few of such systems, if any, achieve satisfactory aerobic bacterial action, as no adequate provision is made for the introduction of air into the complete underground system. An additional problem in hilly or mountainous areas arises in that prior systems require relatively long filter lines which must be installed on grade. This makes installation of such disposal systems almost impossible in mountainous area and very difficult in relatively hilly areas.